1. Field of the Invention
This invention relates to an ignition timing control system for internal combustion engines, and more particularly to an ignition timing control system of this kind, which controls the ignition timing of the engine cylinder by cylinder.
2. Prior Art
Conventionally, there has been proposed, e.g. by Japanese Patent Publication (Kokoku) No. 3-20596, a method of detecting indicated mean effective pressure of each cylinder, determining a variation in the indicated mean effective pressure of each cylinder between operating cycles of the cylinder from the detected values of the indicated means effective pressure, and controlling the ignition timing of the cylinder based on the determined variation in the indicated mean effective pressure so as to reduce the combustion toughness of the engine.
The proposed method, however, requires the use of a combustion pressure sensor for each cylinder, resulting in a complicated construction of the whole ignition control system and an increased manufacturing cost.